An under-road tunnel and fence system supports population increases of the Great Crested Newt in England
Written By Dr. Silviu Petrovan
Senior Research Associate, University of Cambridge
13th September 2021
Photo credit: Mihai Leu
Not all road mitigation targets roadkill
In Europe, newts are far less commonly recorded as roadkill compared to frog or toads. However, road networks can severely disrupt the movement and dispersal of newts, ultimately threatening population viability, such as for the Great Crested Newt in England. Consequently, this species is a frequent target of road mitigation schemes in Britain. However, very little information exists on the effectiveness of such schemes for newts, and almost nothing from a population trend perspective.
Novel monitoring techniques can be very successful
We used specially adapted time-lapse cameras and a custom image analysis tool to monitor the use and effectiveness of a new multi-tunnel and fence system over four years by two newt species and two anuran species. Before construction, the site in northern England had multiple ponds on both sides of the road. As part of the mitigation, all amphibians were transferred to a series of new ponds while the rest of the site was destroyed before some ponds were reinstated and others replanted. Two pairs of ACO climate-type tunnels (50 cm diameter, 24 m long) were installed under the road and a fence system was installed to funnel the amphibians to the tunnels. The number of amphibians in the networks of ponds was assessed before-and-after road construction and the data was used to evaluate the effectiveness of mitigation.
The customised cameras recorded images every 15 seconds (5700 images/day/camera) for 56-65 days per year split between spring and autumn. Cameras were able to record all amphibian movements in the tunnels, including those individuals that made U-turns. Understanding U-turns inside the tunnel is useful both as an indication of the potential for improvement in the design of the system and as a behavioural indication of tunnel acceptance. The automated analysis of the images removed nearly 90% of empty images, greatly reducing the time and cost for image analysis.
High tunnel usage and population growth
Over the four years of monitoring, a total of 565 Great Crested Newts (mostly juveniles), 228 Smooth Newts, 69 Common Frogs and 189 Common Toads were observed in the tunnels. Juvenile frogs or toads were not recorded in the tunnels, likely because they dispersed from ponds at a time when no monitoring took place (i.e. summer months). The fenced road section around the tunnels was checked every 4-5 days during the monitoring period but no amphibians were observed killed or alive on the road surface. Several mammal species were also recorded using the tunnels, including some of conservation concern such as West European Hedgehog and European Otters, both previously unknown to be present at the site. Both species suffer extensive road mortality in Britain.
Figure 1. Male Great Crested Newt crossing under the road via the climate tunnels and recorded with the customised cameras. Notice the timestamp; unlike frogs and toads, most newts, including this one, were using the tunnels in autumn to disperse away from ponds rather than spring for breeding migrations.
Across all years and seasons, the average rate of successful tunnel crossing by adult and juvenile Great Crested Newts was 74.5% and 70.2%, respectively. Interestingly, while most Great Crested Newts moved through the tunnels at night, with peak activity around midnight, Smooth Newts used the tunnel throughout the 24-h period.
The number of water bodies that hosted amphibians increased rapidly after the tunnels and fences were installed. Amphibians used the tunnels to move across the road from the translocation ponds and colonised nine of the ten newly built water management ponds that were created in the project area on both sides of the road. The population of Great Crested Newts in the area grew from an estimate of 59 individuals in 2014 to 300 individuals in 2017. Peak estimates from six repeated annual counts using torch surveys also increased for great crested newts adults from 45 in 2014 to 70 in 2015, 130 in 2016 and 198 in 2017. Similar increases in peak count were observed for Smooth Newts and Common Toads. Interestingly, the population of Common Frogs in the area remained very low.
Most amphibians that entered the tunnels successfully used them to move to the other side of the road, despite substantial evidence of mitigation rejection and U-turn movements inside the tunnels. The road fence prevented amphibian road mortality while site integrity was re-established via the wildlife passage system, allowing amphibians to colonise multiple new ponds across the road. Unlike frogs and toads, tunnel usage by newts was strongly autumn based, suggesting road mitigation for newts should mainly target newt dispersal between breeding areas and thus ensure there are suitable breeding ponds and hibernation sites on both sides of the road. The Great Crested Newt population increased rapidly over the course of the monitoring period, a strong indicator that, together with habitat improvements, the road tunnel and fence system were effective as a population conservation measure.
Author information:
Dr. Silviu Petrovan, Senior Research Associate, University of Cambridge, UK and Trustee at Froglife Trust
Source:
Jarvis, L.E., Hartup, M. & Petrovan, S.O. Road mitigation using tunnels and fences promotes site connectivity and population expansion for a protected amphibian. Eur J Wildl Res 65, 27 (2019). https://doi.org/10.1007/s10344-019-1263-9
Editor:
Daniela Araya Gamboa
Cite this summary:
Petrovan, S. (2021). An under-road tunnel adn fence system supports population increases of the Great Crested Newt in England. Edited by Araya Gamboa, D. TransportEcology.info, Accessed at: https://transportecology.info/research/great-crested-newt-tunnelfencesystem [Date accessed].
